Generally, a flash memory device is a nonvolatile semiconductor memory device capable of electrically performing program and erase operations. The flash memory device is receiving great attentions because of its properties of high capacity and high speed when being applied to high capacity storage devices or code memories of the latest mobile devices. The flash memory device may be classified into a NAND type flash memory and a NOR type flash memory. Among them, a cell array of the NOR type flash memory device has a structure where a plurality of memory cells are connected in parallel to one bit line. On the contrary, the NAND type flash memory has a structure where a plurality of memory cells are connected in series to one bit line.
The NOR type flash memory device stores codes for controlling internal operations. Accordingly, the NOR type flash memory device reads stored codes and uses the stored codes to perform controlling of write, read, and verify operations. The NOR type flash memory device controls various kinds of operations according to code reading, such that time delay may occur.
The NOR type flash memory device performs a read operation for verification, that is, a verify read operation, between code reading operations when a verify operation is performed. The NOR type flash memory device supplies a voltage to a memory cell in order to perform a verify read operation. The NOR type flash memory device requires a setup time (time for changing a memory cell voltage due to a voltage supply) and a recovery time (time for recovering a memory cell voltage). Accordingly, in the NOR type flash memory, time delay occurs because of the setup time and the recovery time during a verify operation. Moreover, the NOR type flash memory performs a code reading operation through a normal read operation and then performs a verify operation in the next step such that continuous read verify operations are impossible. In the NOR type flash memory, memory cells for performing a read operation are distinguished from memory cells for performing a code operations. Therefore, in order to perform a verify operation during a read operation, a code reading operation needs to be performed using additional memory cells instead of memory cells where data are stored.
As a result, time delay occurs because of a code reading operation in the NOR type flash memory.